SOHC.co.uk Forums > CB750

Poor running

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Fordy:
Hi, Can anyone help, I'm at my wits end. My 750K6 runs lovely when cold, but when it gets warmed up it will not run smooth at low revs, it still ticks over nice, open the throttle to accelerate and its smooth as silk again, settle down to a constant speed for speed limits and it runs like a bag of spanners again.
I have replaced all the jets, float needles and seats, slide needles and seats, checked carb balance which are all at a constant 10psi @ 1400 revs. replaced plugs and caps just in case timing is bang on.
But still no different.
Help!!!!!!!

Bitsa (Ralph Wright - RIP):
Sounds like its running rich to me have you done the float heights,clean filter etc.Has it standard pipes,whats the needles set at etc
Cheers
Bitsa

Fordy:
Hi
Yes done float heights at 26mm. Fitted a new filter and the needles are set in 3rd ( middle).
Thought I might try replacing condensers, points are good.
Worth a try?

Waggles:
Agree with Bitsa, it does sound like rich mixture, what do the plugs look like?

It could be condensor(s) breaking down when hot but then I would expect it to run rough all the time when hot regardless of throttle opening. Wouldn't do any harm to replace them though particularly if they are old. If the spark is on the weak side it can sell you a dummy and make a minor carb issue much worse.

Leads me to think carburation and at the lower end of the scale what do you have the slow running screws set at?

Fordy:
Slow jets are set about 1 1/8 out. When I got it the old guy (68) had been running a yoshi straight thru pipe on it but put a brand new motad on to sell it, I thought the poor running was because it had been jetted up, thats why I put new jets in, (bought before I checked, idiot !!!) Yes the old plugs were sooted up.

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